Ultra wideband communication system, method, and device with low noise pulse formation

ABSTRACT

An ultra-wide band (UWB) waveform generator and encoder for use in a UWB digital communication system. The encoder multiplies each data bit by an n-bit identifying code, (e.g., a user code), resulting in a stream of bits corresponding to each data bit. This stream of bits is referred to as the original codeword. The original codeword is passed onto the UWB waveform generator for generation of a UWB waveform that can be transmitted via an antenna. The UWB waveform is made up of shaped wavelets. In one embodiment, the wavelets are bi-phase wavelets, and the UWB waveform generator uses a two-stage differential mixer and a pulse generator. The first stage combines the pulses from the pulse generator with a first derivative codeword derived from the original codeword. The output of this first stage is a wavelet, which is used as input to the second differential mixer along with a second derivative codeword also derived from the original codeword and orthogonal to the first derivative codeword. The output of the second mixer is a wavelet, which represents an inversion of the original codeword. This wavelet is then passed on to an inverting amplifier before it is transmitted via an antenna. By using two derivative codewords at one-half the chipping rate of the original codeword, less power is consumed. An advantage of the two stage mixer system is that it suppresses the noise generated and transmitted by the system.

CROSS REFERENCE TO RELATED PATENT DOCUMENTS

[0001] The present document contains subject matter related to thatdisclosed in commonly owned, co-pending application Ser. No. 09/209,460filed Dec. 11, 1998, entitled ULTRA WIDE BANDWIDTH SPREAD-SPECTRUMCOMMUNICATIONS SYSTEM (Attorney Docket No. 10188-0001-8); Ser. No.09/633,815 filed Aug. 7, 2000, entitled ELECTRICALLY SMALL PLANAR UWBANTENNA (Attorney Docket No.10188-0005-8); application Ser. No.09/563,292 filed May 3, 2000, entitled PLANAR ULTRA WIDE BAND ANTENNAWITH INTEGRATED ELECTRONICS (Attorney Docket No. 10188-0006-8);Application Serial No. 60/207,225 filed May 26, 2000, entitledULTRAWIDEBAND COMMUNICATION SYSTEM AND METHOD (Attorney Docket No.192408US8PROV); application Ser. No. ______ filed Oct. 10, 2000,entitled ANALOG SIGNAL SEPARATOR FOR UWB VERSUS NARROWBAND SIGNALS(Attorney Docket No. 192504US8); application Ser. No. ______ filed Oct.10, 2000, entitled ULTRA WIDE BANDWIDTH NOISE CANCELLATION MECHANISM ANDMETHOD (Attorney Docket No.193517US8); Application Serial No. 60/217,099filed Jul. 10, 2000, entitled MULTIMEDIA WIRELESS PERSONAL AREA NETWORK(WPAN) PHYSICAL LAYER SYSTEM AND METHOD (Attorney DocketNo.194308US8PROV); application Ser. No. ______ filed Oct. 10, 2000,entitled SYSTEM AND METHOD FOR BASEBAND REMOVAL OF NARROWBANDINTERFERENCE IN ULTRA WIDEBAND SIGNALS (Attorney Docket No.194381US8);application Ser. No. ______ filed Oct. 10, 2000, entitled MODECONTROLLER FOR SIGNAL ACQUISITION AND TRACKING IN AN ULTRA WIDEBANDCOMMUNICATION SYSTEM (Attorney Docket No. 194588US8); application Ser.No. ______ filed Oct. 10, 2000, entitled ULTRA WIDEBAND COMMUNICATIONSYSTEM, METHOD, AND DEVICE WITH LOW NOISE PULSE FORMATION (AttorneyDocket No. 195268US8); application Ser. No. ______ filed Oct. 10, 2000,entitled ULTRA WIDE BANDWIDTH SYSTEM AND METHOD FOR FAST SYNCHRONIZATION(Attorney Docket No. 195269US8); application Ser. No. ______ filed Oct.10, 2000, entitled ULTRA WIDE BANDWIDTH SYSTEM AND METHOD FOR FASTSYNCHRONIZATION USING SUB CODE SPINS (Attorney Docket No. 195272US8);application Ser. No. ______ filed Oct. 10, 2000, entitled ULTRA WIDEBANDWIDTH SYSTEM AND METHOD FOR FAST SYNCHRONIZATION USING MULTIPLEDETECTION ARMS (Attorney Docket No. 195273US8); application Ser. No.______ filed Oct. 10, 2000, entitled A LOW POWER, HIGH RESOLUTION TIMINGGENERATOR FOR ULTRA-WIDE BANDWIDTH COMMUNICATION SYSTEMS (AttorneyDocket No. 195670US8); application Ser. No. ______ filed Oct. 10, 2000,entitled METHOD AND SYSTEM FOR ENABLING DEVICE FUNCTIONS BASED ONDISTANCE INFORMATION (Attorney Docket No. 195671US8); application Ser.No. ______ filed Oct. 10, 2000, entitled CARRIERLESS ULTRA WIDEBANDWIRELESS SIGNALS FOR CONVEYING APPLICATION DATA (Attorney Docket No.196108US8); application Ser. No. ______ filed Oct. 10, 2000, entitledSYSTEM AND METHOD FOR GENERATING ULTRA WIDEBAND PULSES (Attorney DocketNo. 197023US8); application Ser. No. ______ filed Oct. 10, 2000,entitled ULTRA WIDEBAND COMMUNICATION SYSTEM, METHOD, AND DEVICE WITHLOW NOISE RECEPTION (Attorney Docket No.197024US8); and application Ser.No. ______ filed Oct. 10, 2000, entitled LEAKAGE NULLING RECEIVERCORRELATOR STRUCTURE AND METHOD FOR ULTRA WIDE BANDWIDTH COMMUNICATIONSYSTEM (Attorney Docket No. 1541.1001/GMG), the entire contents of eachof which being incorporated herein by reference.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The present invention relates to ultra wideband (UWB) radiocommunication systems, methods and devices used in the system forgenerating UWB waveforms that include wavelets that are modulated toconvey digital data over a wireless radio communication channel usingultra wideband signaling techniques.

[0004] 2. Description of the Background

[0005] There are numerous radio communication techniques to transmitdigital data over a wireless channel. These techniques include thoseused in mobile telephone systems, pagers, remote data collectionsystems, and wireless networks for computers, among others. Mostconventional wireless communication techniques modulate the digital dataonto a high-frequency carrier that is then transmitted via an antennainto space.

[0006] Ultra wideband (UWB) communications systems transmit carrierlesshigh data rate, low power signals. Since a carrier is not used, thetransmitted waveforms themselves contain the information beingcommunicated. Accordingly, conventional UWB systems transmit pulses, theinformation to be communicated is contained in the pulses themselves,and not on a carrier.

[0007] Conventional UWB communication systems send a sequence ofidentical pulses, the timing of which carries the information beingcommunicated, for example, as described by Fullerton and Cowie (U.S.Pat. No. 5,677,927). This technique is known as pulse positionmodulation (PPM). In a PPM scheme, the information in a pulse isobtained by determining an arrival time of the pulse at a receiverrelative to other pulses. For example, given an exemplary time window,if a pulse is received at the beginning of that time window, thereceiver will decode that pulse as a ‘1,’ whereas if the pulse isreceived at the end of that same time window, the receiver will decodethat pulse as a ‘0.’

[0008] Several problems arise with this technique, however, asrecognized by the present inventors. First, it is not as efficient asother techniques, for example, sending non-inverted and inverted pulseswhere 3 dB less radiated power is required to communicate in the samememory-less Gaussian white noise channel. Second, reflections fromobjects in the vicinity of the transmitter and receiver can cause apulse that was supposed to be at the beginning of the time window, toappear in at the end of time window, or even in the time window of asubsequent pulse.

[0009] As a result, it would be advantageous if the data stream to betransmitted could be encoded by changing a shape of the UWB pulse ratherthan a position of the UWB pulse as with conventional systems. Forexample, if the UWB pulses had two possible shapes, a single time framecould be used encode a single bit of data, rather than the two timeframes (i.e., early and late) that would be required by a PPM system. Inthe present UWB communications system, and related co-pendingapplication Ser. No. 09/209,460 filed May 14, 1998, entitled ULTRA WIDEBANDWIDTH SPREAD SPECTRUM COMMUNICATIONS SYSTEM (Attorney Docket No.10188-0001-8), information is carried by the shape of the pulse, or theshape in combination with its position in the pulse-sequence.

[0010] Conventional techniques for generating pulses include a varietyof techniques, for example, networks of transmission lines such as thosedescribed in co-pending application Ser. No. 09/209,460 filed May 14,1998, entitled ULTRA WIDE BANDWIDTH SPREAD SPECTRUM COMMUNICATIONSSYSTEM (Attorney Docket No. 10188-0001-8). One of the problemsassociated with this technique is that the transmission lines take upsizeable space and accordingly, are not amenable to integration on amonolithic integrated circuit. Given that a key targeted use of UWBsystems is for small, handheld mobile devices such as personal digitalassistants (PDAs) and mobile telephones, space is at a premium whendesigning UWB systems. Furthermore, it is highly desirable to integratethe entire radio onto a single monolithic integrated circuit in order tomeet the cost, performance, and volume-production requirements ofconsumer electronics devices.

[0011] A key attribute that must be maintained, however, regardless ofhow the information is carried, is that no tones can be present. Inother words, the average power spectrum must be smooth and void of anyspikes. In generating these UWB pulse streams, however, non-ideal deviceperformance can cause tones to pass through to the antenna and to beradiated. In particular, switches, gates, and analog mixers that areused to generate pulses are well known to be non-ideal devices. Forexample, leakage is a problem. A signal that is supposed to be blockedat certain times, for example, can continue to leak through. Similarly,non-ideal symmetry in positive and negative voltages or currentdirections can allow tones be generated or leak through. In anotherexample, the output of a mixer can include not only the desired UWBpulse stream, but also spikes in the frequency domain at the clockfrequency and its harmonics, as well as other noise, due to leakagebetween the RF, LO, and IF ports. This is problematic since one of thedesign objectives is to generate a pulse stream that will not interferewith other communications systems.

[0012] Similar problems to those discussed above regarding transmittersare also encountered in UWB receivers. Mixers are used in UWB receiversto mix the received signal with known waveforms so that the transmitteddata may be decoded. As discussed above, the spectral spikes (DC andotherwise) introduced by the non-ideal analog mixers can make decodingof only moderately weak signals difficult or impossible.

[0013] Furthermore, UWB receivers often suffer from leakage of the UWBsignal driving the mixer due to the large amplitude of the drive signaland its very close proximity to the antenna as well as adjacentcomponents. These UWB drive signals can radiate into space and bereceived by the antenna where it can jam the desired UWB signal, or becoupled via the substrate. This reception of the drive signal being usedto decode the received signal can therefore cause a self-jammingcondition wherein the desired signal becomes unintelligible.

[0014] The challenge, then, as presently recognized, is to develop ahighly integratable approach for generating shape-modulated waveletsequences that can be used in a UWB communications system to encode,broadcast, receive, and decode a data stream. It would be advantageousif the data stream to be transmitted could be encoded by changing ashape of the UWB pulse rather than a position of the UWB pulse as withconventional systems.

[0015] Furthermore, the challenge is to build such a wavelet generatorwhere the smooth power spectrum calculated by using ideal components, isrealized using non-ideal components. In other words, an approach togenerating and receiving UWB waveforms that does not generate unwantedfrequency domain spikes as a by-product, spikes that are prone tointerfere with other communications devices or cause self-jamming, wouldbe advantageous.

[0016] It would also be advantageous if the UWB waveform generationapproach were to minimize the power consumption because many of thetargeted applications for UWB communications are in handheldbattery-operated mobile devices.

SUMMARY OF THE INVENTION

[0017] Accordingly, one object of this invention is to provide a novelprogrammable wavelet generator for generating a variety of wavelets foruse in a UWB communication system that addresses the above-identifiedand other problems with conventional devices.

[0018] The inventors of the present invention have recognized that byimplementing a two-mixer approach to generating UWB waveforms, that thenoise leakage from the non-ideal analog mixers can be whitened, therebyavoiding the interference problems caused by conventional single-mixerapproaches. The present inventors have provided a contrarian approach ofsuppressing mixer-created interference by using a second mixer.

[0019] The inventors of the present invention have also recognized thatby creating a UWB waveform by mixing two derivative data streams runningat one-half a chipping rate of the original data stream, that powerconsumption can be reduced within the UWB device.

[0020] These and other objects are achieved according to the presentinvention by providing a novel circuit for generating wavelets that ishighly integratable, and a two-mixer approach for using the wavelets forencoding a data stream while canceling the leakage introduced bynon-ideal analog mixers.

[0021] In one embodiment, the wavelet generator uses two pulses, anearly pulse and a late pulse, from a pulse generation circuit, that whenmixed with a positive or a negative voltage in a conventionaldifferential mixer, creates a wavelet that is either positive ornegative (i.e., non-inverted or inverted). By mixing the pulse generatoroutput with a stream of data (positive voltage for a ‘1’, negativevoltage for a ‘0’), a waveform having a sequence of wavelets is createdare transmitted as a UWB signal. In a preferred embodiment, the mixer isa Gilbert cell mixer. In other embodiments, the mixer is, for example, adiode bridge mixer, or any electrically, optically, ormechanically-driven configuration of switching devices including, forexample, an FET, a heterojunction, a bulk semiconductor device, or amicro-machine device.

[0022] In one embodiment of the two-mixer configuration for creating theUWB waveform, the noise introduced by the analog devices is canceled bywhitening the output of the first mixer by mixing it with a white signalat the second mixer. In this embodiment, the data stream is divided intotwo derivative data streams, one of which is mixed with the pulsegenerator at the first analog mixer, and the other is mixed with thewavelets created by the first mixer. Since the derivative data streamsare sufficiently white, mixing the result of the first mixer with thesecond derivative data stream will spread the unwanted spikes introducedby the first mixer. Moreover, in this embodiment, the two derivativedata streams are at one-half the chipping rate of the original datastream, thereby reducing the power consumption by running at a lowerclock rate.

[0023] In a second embodiment of the two-mixer configuration, a noisysignal is applied through an exclusive OR (XOR) to a single data stream.The result is then mixed with the pulse generator to create the waveletsat a first mixer. The result of the first mixer is then mixed with thenoisy signal at the second mixer, again, to spread the unwanted spikesintroduced by the first mixer.

[0024] Consistent with the title of this section, the above summary isnot intended to be an exhaustive discussion of all the features orembodiments of the present invention. A more complete, although notnecessarily exhaustive description of the features and embodiments ofthe invention is found in the section entitled “DESCRIPTION OF THEPREFERRED EMBODIMENTS” as well as the entire document generally.

BRIEF DESCRIPTION OF THE DRAWINGS

[0025]FIG. 1a is a block diagram of an ultra-wide band (UWB)transceiver, according to the present invention;

[0026]FIG. 1b is a diagram for illustrating the operation of thetransceiver of FIG. 1a, according to the present invention;

[0027]FIG. 2 is a block diagram of the transceiver of FIG. 1a, thatmanipulates a shape of UWB pulses, according to the present invention;

[0028]FIG. 3 is a schematic diagram of a general-purposemicroprocessor-based or digital signal processor-based system, which canbe programmed by a skilled programmer to implement the features of thepresent invention;

[0029]FIG. 4 is a flow chart of a process implementing an algorithm usedas a startup procedure for generating two derived codewords from anoriginal codeword according to the present invention;

[0030]FIG. 5 illustrates a process flow for splitting a single originaldata stream into 2 data streams including even bits and odd bits of theoriginal data stream, respectively, at one-half the chipping rate of theoriginal data stream according to the present invention;

[0031]FIG. 6 is a schematic diagram of a logic circuit for creating twoderived codewords from an even-bit data stream and an odd-bit datastream produced by the splitter illustrated in FIG. 5;

[0032]FIG. 7 is a schematic diagram of a two-stage differential mixerfor generating low-noise wavelets according to one embodiment of thepresent invention;

[0033]FIG. 8 is a schematic diagram of a circuit used to generate anearly pulse and a late pulse according to one embodiment of the presentinvention;

[0034]FIG. 8A is a schematic diagram of an AND gate used in the circuitof FIG. 8 according to one embodiment of the present invention;

[0035]FIG. 9A is a schematic of a Gilbert cell differential mixer;

[0036]FIG. 9B is an illustration of the early and late pulses generatedby the pulse generating circuit of FIG. 8;

[0037]FIG. 9C illustrates a bi-phase wavelet generated by the pulsegenerating circuit of FIG. 8 when the incoming data bit is high;

[0038]FIG. 9D illustrates a bi-phase wavelet generated by the pulsegenerating circuit of FIG. 8 when the incoming data bit is low;

[0039]FIG. 9E is a schematic diagram of a FET bridge differential mixer;

[0040]FIG. 9F is a schematic diagram of a diode bridge differentialmixer;

[0041]FIG. 10 is an exemplary timing chart illustrating the inputs andoutputs of the first differential mixer of the two-stage mixer accordingto one embodiment of the present invention;

[0042]FIGS. 11A and 11B are graphs that illustrate the spectral spikesproduced by non-ideal analog devices and the whitening of those spikes;

[0043]FIG. 12 is an exemplary timing chart illustrating the inputs andoutputs of the second differential mixer of the two-stage mixeraccording to one embodiment of the present invention;

[0044]FIG. 13 is a schematic diagram of a two-stage differential mixerfor generating low-noise wavelets by mixing the data stream with noiseaccording to one embodiment of the present invention; and

[0045]FIG. 14 is a schematic diagram of a generalized two-stage mixingcircuit for achieving noise cancellation in an ultra widebandtransmitter according to the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0046]FIG. 1a is a block diagram of an ultra-wide band (UWB)transceiver. In FIG. 1a, the transceiver includes three majorcomponents, namely, receiver 11, radio controller and interface 9, andtransmitter 13. Alternatively, the system may be implemented as aseparate receiver 11 and radio controller and interface 9, and aseparate transmitter 13 and radio controller and interface 9. The radiocontroller and interface 9 serves as a media access control (MAC)interface between the UWB wireless communication functions implementedby the receiver 11 and transmitter 13 and applications that use the UWBcommunications channel for exchanging data with remote devices.

[0047] The receiver 11 includes an antenna 1 that converts a UWBelectromagnetic waveform into an electrical signal (or optical signal)for subsequent processing. The UWB signal is generated with a sequenceof shape-modulated wavelets, where the occurrence times of theshape-modulated wavelets may also be modulated. For analog modulation,at least one of the shape control parameters is modulated with theanalog signal. More typically, the wavelets take on M possible shapes.Digital information is encoded to use one or a combination of the Mwavelet shapes and occurrence times to communicate information.

[0048] In one embodiment of the present invention, each waveletcommunicates one bit, for example, using two shapes such as bi-phase. Inother embodiments of the present invention, each wavelet may beconfigured to communicate nn bits, where M≧2^(nn). For example, fourshapes may be configured to communicate two bits, such as withquadrature phase or four-level amplitude modulation. In anotherembodiment of the present invention, each wavelet is a “chip” in a codesequence, where the sequence, as a group, communicates one or more bits.The code can be M-ary at the chip level, choosing from M possible shapesfor each chip.

[0049] At the chip, or wavelet level, embodiments of the presentinvention produce UWB waveforms. The UWB waveforms are modulated by avariety of techniques including but not limited to: (i) bi-phasemodulated signals (+1, −1), (ii) multilevel bi-phase signals (+1, −1,+a1, −a1, +a2, −a2, . . . , +aN, −aN), (iii) quadrature phase signals(+1, −1, +j, −j), (iv) multi-phase signals (1, −1, exp(+jπ/N),exp(−jπ/N), exp(+jπ2/N), exp(−jπ2/N), . . . , exp(+j(N−1)/N),exp(−jπ(N−1)/N)), (v) multilevel multi-phase signals (a_(i)exp(j2πβ/N)|a_(i)ε{1, a1, a2, . . . , aK}, βε{0, 1, . . . , N−1}), (vi)frequency modulated pulses, (vii) pulse position modulation (PPM)signals (possibly same shape pulse transmitted in different candidatetime slots), (viii) M-ary modulated waveforms g_(B) _(i) (t) withB_(i)ε{1, . . . , M}, and (ix) any combination of the above waveforms,such as multi-phase channel symbols transmitted according to a chirpingsignaling scheme. The present invention, however, is applicable tovariations of the above modulation schemes and other modulation schemes(e.g., as described in Lathi, “Modern Digital and Analog CommunicationsSystems,” Holt, Rinehart and Winston, 1998, the entire contents of whichis incorporated by reference herein), as will be appreciated by thoseskilled in the relevant art(s).

[0050] Some exemplary waveforms and characteristic equations thereofwill now be described. The time modulation component, for example, canbe defined as follows. Let t_(i) be the time spacing between the(i−1)^(th) pulse and the i^(th) pulse. Accordingly, the total time tothe i^(th) pulse is $T_{i} = {\sum\limits_{j = 0}^{i}\quad {t_{j}.}}$

[0051] The signal T_(i) could be encoded for data, part of a spreadingcode or user code, or some combination thereof. For example, the signalT_(i) could be equally spaced, or part of a spreading code, where T_(i)corresponds to the zero-crossings of a chirp, i.e., the sequence ofT_(i)'s, and where $T_{i} = \sqrt{\frac{i - a}{k}}$

[0052] for a predetermined set of a and k. Here, a and k may also bechosen from a finite set based on the user code or encoded data.

[0053] An embodiment of the present invention can be described usingM-ary modulation. Equation 1 below can be used to represent a sequenceof exemplary transmitted or received pulses, where each pulse is a shapemodulated UWB wavelet, g_(B) _(i) (t−T_(i)). $\begin{matrix}{{x(t)} = {\sum\limits_{i = 0}^{\infty}\quad {g_{B_{i}}\left( {t - T_{i}} \right)}}} & (1)\end{matrix}$

[0054] In the above equation, the subscript i refers to the i^(th) pulsein the sequence of UWB pulses transmitted or received. The waveletfunction g has M possible shapes, and therefore B_(i) represents amapping from the data, to one of the M-ary modulation shapes at thei^(th) pulse in the sequence. The wavelet generator hardware (e.g., theUWB waveform generator 17) has several control lines (e.g., coming fromthe radio controller and interface 9) that govern the shape of thewavelet. Therefore, B_(i) can be thought of as including a lookup-tablefor the M combinations of control signals that produce the M desiredwavelet shapes. The encoder 21 combines the data stream and codes togenerate the M-ary states. Demodulation occurs in the waveformcorrelator 5 and the radio controller and interface 9 to recover to theoriginal data stream. Time position and wavelet shape are combined intothe pulse sequence to convey information, implement user codes, etc.

[0055] In the above case, the signal is comprised of wavelets from i=1to infinity. As i is incremented, a wavelet is produced. Equation 2below can be used to represent a generic wavelet pulse function, whoseshape can be changed from pulse to pulse to convey information orimplement user codes, etc.

g _(B) _(i) (t)=Re(B _(i,1))·ƒ_(B) _(i,2) _(,B) _(i,3) _(, . . .)(t)+Im(B _(i,1))·h _(B) _(i,2) _(,B) _(i,3) _(, . . . () t)  (2)

[0056] In the above equation, function ƒ defines a basic wavelet shape,and function h is simply the Hilbert transform of the function ƒ. Theparameter B_(i,1) is a complex number allowing the magnitude and phaseof each wavelet pulse to be adjusted, i.e., B_(i,1)=a_(i)<θ_(i), wherea₁ is selected from a finite set of amplitudes and θ_(i) is selectedfrom a finite set of phases. The parameters {B_(i,2), B_(i,3), . . . }represent a generic group of parameters that control the wavelet shape.

[0057] An exemplary waveform sequence x(t) can be based on a family ofwavelet pulse shapes ƒ that are derivatives of a Guassian waveform asdefined by Equation 3 below. $\begin{matrix}{{f_{B_{i}}(t)} = {{\Psi \left( {B_{i,2},B_{i,3}} \right)}\left( {\frac{^{B_{i,3}}}{t^{B_{i,3}}}^{- {\lbrack{B_{i,2}t}\rbrack}^{2}}} \right)}} & (3)\end{matrix}$

[0058] In the above equation, the function Ψ( ) normalizes the peakabsolute value of ƒ_(B) _(i) (t) to 1. The parameter B_(i,2) controlsthe pulse duration and center frequency. The parameter B_(i,3) is thenumber of derivatives and controls the bandwidth and center frequency.

[0059] Another exemplary waveform sequence x(t) can be based on a familyof wavelet pulse shapes ƒ that are Gaussian weighted sinusoidalfunctions, as described by Equation 4 below.

ƒ_(B) _(i,2) _(,B) _(i,3) _(,B) _(i,4) =ƒ_(ω) _(i) _(,k) _(i) _(,b) _(i)(t)=e ^(−[b) ^(_(i)) ^(t]) ² sin(ω_(i) t+k _(i) t ²).  (4)

[0060] In the above equation, b_(i) controls the pulse duration, ω_(i)controls the center frequency, and k_(i) controls a chirp rate. Otherexemplary weighting functions, beside Gaussian, that are also applicableto the present invention include, for example, Rectangular, Hanning,Hamming, Blackman-Harris, Nutall, Taylor, Kaiser, Chebychev, etc.

[0061] Another exemplary waveform sequence x(t) can be based on a familyof wavelet pulse shapes ƒ that are inverse-exponentially weightedsinusoidal functions, as described by Equation 5 below. $\begin{matrix}{{{g_{B_{i}}(t)} = {\left( {\frac{1}{^{\frac{- {({t - {t1}_{i}})}}{{.3}*t_{r_{i}}}} + 1} - \frac{1}{^{\frac{- {({t - {t2}_{i}})}}{{.3}*t_{f_{i}}}} + 1}} \right) \cdot {\sin \left( {\theta_{i} + {\omega_{i}t} + {k_{i}t^{2}}} \right)}}}\quad {{{where}\quad \left\{ {B_{i,2},B_{i,3},B_{i,4},B_{i,5},B_{i,6},B_{i,7},B_{i,8}} \right\}} = \left\{ {{t1}_{i},{t2}_{i},t_{r_{i}},t_{f_{i}},\theta_{i},\omega_{i},k_{i}} \right\}}} & (5)\end{matrix}$

[0062] In the above equation, the leading edge turn on time iscontrolled by t₁, and the turn-on rate is controlled by t_(r). Thetrailing edge turn-off time is controlled by t₂, and the turn-off rateis controlled by t_(ƒ). Assuming the chirp starts at t=0 and T_(D) isthe pulse duration, the starting phase is controlled by θ, the startingfrequency is controlled by ω, the chirp rate is controlled by k, and thestopping frequency is controlled by ω+kT_(D). An example assignment ofparameter values is ω=1, t_(r)=t_(ƒ)=0.25, t₁=t_(r)/0.51, andt₂=T_(D)−t_(r)/9.

[0063] A feature of the present invention is that the M-ary parameterset used to control the wavelet shape is chosen so as to make a UWBsignal, wherein the center frequency f_(c) and the bandwidth B of thepower spectrum of g(t) satisfies 2ƒ_(c)>B>0.25ƒ_(c). It should be notedthat conventional equations define in-phase and quadrature signals(e.g., often referred to as I and Q) as sine and cosine terms. Animportant observation, however, is that this conventional definition isinadequate for UWB signals. The present invention recognizes that use ofsuch conventional definition may lead to DC offset problems and inferiorperformance.

[0064] Furthermore, such inadequacies get progressively worse as thebandwidth moves away from 0.25ƒ_(c) and toward 2ƒ_(c). A key attributeof the exemplary wavelets (or e.g., those described in co-pending U.S.patent application Ser. No. 09/209,460) is that the parameters arechosen such that neither ƒ nor h in Equation 2 above has a DC component,yet ƒ and h exhibit the required wide relative bandwidth for UWBsystems.

[0065] Similarly, as a result of B>0.25ƒ_(c), it should be noted thatthe matched filter output of the UWB signal is typically only a fewcycles, or even a single cycle. For example, the parameter n in Equation3 above may only take on low values (e.g., such as those described inco-pending U.S. patent application Ser. No. 09/209,460).

[0066] The compressed (i.e., coherent matched filtered) pulse width of aUWB wavelet will now be defined with reference to FIG. 1b. In FIG. 1b,the time domain version of the wavelet thus represents g(t) and theFourier transform (FT) version is represented by G(ω). Accordingly, thematched filter is represented as G*(ω), the complex conjugate, so thatthe output of the matched filter is P(ω)=G(ω)·G*(ω). The output of thematched filter in the time domain is seen by performing an inverseFourier transform (IFT) on P(ω) so as to obtain p(t), the compressed ormatched filtered pulse. The width of the compressed pulse p(t) isdefined by T_(C), which is the time between the points on the envelopeof the compressed pulse E(t) that are 6 dB below the peak thereof, asshown in FIG. 1b. The envelope waveform E(t) may be determined byEquation 6 below.

E(t)={square root}{square root over ((p(t)²+(p ^(H)(t)²)}  (6)

[0067] where p^(H)(t) is the Hilbert transform of p(t).

[0068] Accordingly, the above-noted parameterized waveforms are examplesof UWB wavelet functions that can be controlled to communicateinformation with a large parameter space for making codes with goodresulting autocorrelation and cross-correlation functions. For digitalmodulation, each of the parameters is chosen from a predetermined listaccording to an encoder that receives the digital data to becommunicated. For analog modulation, at least one parameter is changeddynamically according to some function (e.g., proportionally) of theanalog signal that is to be communicated.

[0069] Referring back to FIG. 1a, the electrical signals coupled inthrough the antenna 1 are passed to a radio front end 3. Depending onthe type of waveform, the radio front end 3 processes the electricsignals so that the level of the signal and spectral components of thesignal are suitable for processing in the UWB waveform correlator 5. TheUWB waveform correlator 5 correlates the incoming signal (e.g., asmodified by any spectral shaping, such as a matched filtering, partiallymatched filtering, simply roll-off, etc., accomplished in front end 3)with different candidate signals generated by the receiver 11, so as todetermine when the receiver 11 is synchronized with the received signaland to determine the data that was transmitted.

[0070] The timing generator 7 of the receiver 11 operates under controlof the radio controller and interface 9 to provide a clock signal thatis used in the correlation process performed in the UWB waveformcorrelator 5. Moreover, in the receiver 11, the UWB waveform correlator5 correlates in time a particular pulse sequence produced at thereceiver 11 with the receive pulse sequence that was coupled in throughantenna 1 and modified by front end 3. When the two such sequences arealigned with one another, the UWB waveform correlator 5 provides highsignal to noise ratio (SNR) data to the radio controller and interface 9for subsequent processing. In some circumstances, the output of the UWBwaveform correlator is the data itself. In other circumstances, the UWBwaveform correlator 5 simply provides an intermediate correlationresult, which the radio controller and interface 9 uses to determine thedata and determine when the receiver 11 is synchronized with theincoming signal.

[0071] In some embodiments of the present invention, whensynchronization is not achieved (e.g., during a signal acquisition modeof operation), the radio controller and interface 9 provides a controlsignal to the receiver 11 to acquire synchronization. In this way, asliding of a correlation window within the UWB waveform correlator 5 ispossible by adjustment of the phase and frequency of the output of thetiming generator 7 of the receiver 11 via a control signal from theradio controller and interface 9. The control signal causes thecorrelation window to slide until lock is achieved. The radio controllerand interface 9 is a processor-based unit that is implemented eitherwith hard wired logic, such as in one or more application specificintegrated circuits (ASICs) or in one or more programmable processors.

[0072] Once synchronized, the receiver 11 provides data to an input port(“RX Data In”) of the radio controller and interface 9. An externalprocess, via an output port (“RX Data Out”) of the radio controller andinterface 9, may then use this data. The external process may be any oneof a number of processes performed with data that is either received viathe receiver 11 or is to be transmitted via the transmitter 13 to aremote receiver.

[0073] During a transmit mode of operation, the radio controller andinterface 9 receives source data at an input port (“TX Data In”) from anexternal source. The radio controller and interface 9 then applies thedata to an encoder 21 of the transmitter 13 via an output port (“TX DataOut”). In addition, the radio controller and interface 9 providescontrol signals to the transmitter 13 for use in identifying thesignaling sequence of UWB pulses. In some embodiments of the presentinvention, the receiver 11 and the transmitter 13 functions may usejoint resources, such as a common timing generator and/or a commonantenna, for example. The encoder 21 receives user coding informationand data from the radio controller and interface 9 and preprocesses thedata and coding so as to provide a timing input for the UWB waveformgenerator 17, which produces UWB pulses encoded in shape and/or time toconvey the data to a remote location.

[0074] The encoder 21 produces the control signals necessary to generatethe required modulation. For example, the encoder 21 may take a serialbit stream and encode it with a forward error correction (FEC) algorithm(e.g., such as a Reed Solomon code, a Golay code, a Hamming code, aConvolutional code, etc.). The encoder 21 may also interleave the datato guard against burst errors. The encoder 21 may also apply a whiteningfunction to prevent long strings of “ones” or “zeros.” The encoder 21may also apply a user specific spectrum spreading function, such asgenerating a predetermined length chipping code that is sent as a groupto represent a bit (e.g., inverted for a “one” bit and non-inverted fora “zero” bit, etc.). The encoder 21 may divide the serial bit streaminto subsets in order to send multiple bits per wavelet or per chippingcode, and generate a plurality of control signals in order to affect anycombination of the modulation schemes as described above (and/or asdescribed in Lathi).

[0075] The radio controller and interface 9 may provide someidentification, such as user ID, etc., of the source from which the dataon the input port (“TX Data In”) is received. In one embodiment of thepresent invention, this user ID may be inserted in the transmissionsequence, as if it were a header of an information packet. In otherembodiments of the present invention, the user ID itself may be employedto encode the data, such that a receiver receiving the transmissionwould need to postulate or have a priori knowledge of the user ID inorder to make sense of the data. For example, the ID may be used toapply a different amplitude signal (e.g., of amplitude “f”) to a fastmodulation control signal to be discussed with respect to FIG. 2, as away of impressing the encoding onto the signal.

[0076] The output from the encoder 21 is applied to a UWB waveformgenerator 17. The UWB waveform generator 17 produces a UWB pulsesequence of pulse shapes at pulse times according to the command signalsit receives, which may be one of any number of different schemes. Theoutput from the UWB generator 17 is then provided to an antenna 15,which then transmits the UWB energy to a receiver.

[0077] In one UWB modulation scheme, the data may be encoded by usingthe relative spacing of transmission pulses (e.g., PPM, chirp, etc.). Inother UWB modulation schemes, the data may be encoded by exploiting theshape of the pulses as described above (and/or as described in Lathi).It should be noted that the present invention is able to combine timemodulation (e.g., such as pulse position modulation, chirp, etc.) withother modulation schemes that manipulate the shape of the pulses.

[0078] There are numerous advantages to the above capability, such ascommunicating more than one data bit per symbol transmitted from thetransmitter 13, etc. An often even more important quality, however, isthe application of such technique to implement spread-spectrum,multi-user systems, which require multiple spreading codes (e.g., suchas each with spike autocorrelation functions, and jointly with low peakcross-correlation functions, etc.).

[0079] In addition, combining timing, phase, frequency, and amplitudemodulation adds extra degrees of freedom to the spreading codefunctions, allowing greater optimization of the cross-correlation andautocorrelation characteristics. As a result of the improvedautocorrelation and cross-correlation characteristics, the systemaccording to the present invention has improved capability, allowingmany transceiver units to operate in close proximity without sufferingfrom interference from one another.

[0080]FIG. 2 is a block diagram of a transceiver embodiment of thepresent invention in which the modulation scheme employed is able tomanipulate the shape and time of the UWB pulses. In FIG. 2, whenreceiving energy through the antenna 1, 15 (e.g., corresponding antennas1 and 15 of FIG. 1a) the energy is coupled in to a transmit/receive(T/R) switch 27, which passes the energy to a radio front end 3. Theradio front end 3 filters, extracts noise, and adjusts the amplitude ofthe signal before providing the same to a splitter 29. The splitter 29divides the signal up into one of N different signals and applies the Ndifferent signals to different tracking correlators 31 ₁-31 _(N). Eachof the tracking correlators 31 ₁-31 _(N) receives a clock input signalfrom a respective timing generator 7 ₁-7 _(N) of a timing generatormodule 7, 19, as shown in FIG. 2.

[0081] The timing generators 7 ₁-7 _(N), for example, receive a phaseand frequency adjustment signal, as shown in FIG. 2, but may alsoreceive a fast modulation signal or other control signal(s) as well. Theradio controller and interface 9 provides the control signals, such asphase, frequency and fast modulation signals, etc., to the timinggenerator module 7, 19, for time synchronization and modulation control.The fast modulation control signal may be used to implement, forexample, chirp waveforms, PPM waveforms, such as fast time scale PPMwaveforms, etc.

[0082] The radio controller and interface 9 also provides controlsignals to, for example, the encoder 21, the waveform generator 17, thefilters 23, the amplifier 25, the T/R switch 27, the front end 3, thetracking correlators 31 ₁-31 _(N) (corresponding to the UWB waveformcorrelator of FIG. 1a), etc., for controlling, for example, amplifiergains, signal waveforms, filter passbands and notch functions,alternative demodulation and detecting processes, user codes, spreadingcodes, cover codes, etc.

[0083] During signal acquisition, the radio controller and interface 9adjusts the phase input of, for example, the timing generator 7 ₁, in anattempt for the tracking correlator 31 ₁ to identify and the match thetiming of the signal produced at the receiver with the timing of thearriving signal. When the received signal and the locally generatedsignal coincide in time with one another, the radio controller andinterface 9 senses the high signal strength or high SNR and begins totrack, so that the receiver is synchronized with the received signal.

[0084] Once synchronized, the receiver will operate in a tracking mode,where the timing generator 7 ₁ is adjusted by way of a continuing seriesof phase adjustments to counteract any differences in timing of thetiming generator 7 ₁ and the incoming signal. However, a feature of thepresent invention is that by sensing the mean of the phase adjustmentsover a known period of time, the radio controller and interface 9adjusts the frequency of the timing generator 7 ₁ so that the mean ofthe phase adjustments becomes zero. The frequency is adjusted in thisinstance because it is clear from the pattern of phase adjustments thatthere is a frequency offset between the timing generator 7 ₁ and theclocking of the received signal. Similar operations may be performed ontiming generators 7 ₂-7 _(N), so that each receiver can recover thesignal delayed by different amounts, such as the delays caused bymultipath (i.e., scattering along different paths via reflecting off oflocal objects).

[0085] A feature of the transceiver in FIG. 2 is that it includes aplurality of tracking correlators 31 ₁-31 _(N). By providing a pluralityof tracking correlators, several advantages are obtained. First, it ispossible to achieve synchronization more quickly (i.e., by operatingparallel sets of correlation arms to find strong SNR points overdifferent code-wheel segments). Second, during a receive mode ofoperation, the multiple arms can resolve and lock onto differentmultipath components of a signal. Through coherent addition, the UWBcommunication system uses the energy from the different multipath signalcomponents to reinforce the received signal, thereby improving signal tonoise ratio. Third, by providing a plurality of tracking correlatorarms, it is also possible to use one arm to continuously scan thechannel for a better signal than is being received on other arms.

[0086] In one embodiment of the present invention, if and when thescanning arm finds a multipath term with higher SNR than another armthat is being used to demodulate data, the role of the arms is switched(i.e., the arm with the higher SNR is used to demodulate data, while thearm with the lower SNR begins searching). In this way, thecommunications system dynamically adapts to changing channel conditions.

[0087] The radio controller and interface 9 receives the informationfrom the different tracking correlators 31 ₁-31 _(N) and decodes thedata. The radio controller and interface 9 also provides control signalsfor controlling the front end 3, e.g., such as gain, filter selection,filter adaptation, etc., and adjusting the synchronization and trackingoperations by way of the timing generator module 7, 19.

[0088] In addition, the radio controller and interface 9 serves as aninterface between the communication link feature of the presentinvention and other higher level applications that will use the wirelessUWB communication link for performing other functions. Some of thesefunctions would include, for example, performing range-findingoperations, wireless telephony, file sharing, personal digital assistant(PDA) functions, embedded control functions, location-findingoperations, etc.

[0089] On the transmit portion of the transceiver shown in FIG. 2, atiming generator 7 ₀ also receives phase, frequency and/or fastmodulation adjustment signals for use in encoding a UWB waveform fromthe radio controller and interface 9. Data and user codes (via a controlsignal) are provided to the encoder 21, which in the case of anembodiment of the present invention utilizing time-modulation, passescommand signals (e.g., Δt) to the timing generator 7 ₀ for providing thetime at which to send a pulse. In this way, encoding of the data intothe transmitted waveform may be performed.

[0090] When the shape of the different pulses are modulated according tothe data and/or codes, the encoder 21 produces the command signals as away to select different shapes for generating particular waveforms inthe waveform generator 17. For example, the data may be grouped inmultiple data bits per channel symbol. The waveform generator 17 thenproduces the requested waveform at a particular time as indicated by thetiming generator 7 ₀. The output of the waveform generator is thenfiltered in filter 23 and amplified in amplifier 25 before beingtransmitted via antenna 1, 15 by way of the T/R switch 27.

[0091] In another embodiment of the present invention, the transmitpower is set low enough that the transmitter and receiver are simplyalternately powered down without need for the T/R switch 27. Also, insome embodiments of the present invention, neither the filter 23 nor theamplifier 25 is needed, because the desired power level and spectrum isdirectly useable from the waveform generator 17. In addition, thefilters 23 and the amplifier 25 may be included in the waveformgenerator 17 depending on the implementation of the present invention.

[0092] A feature of the UWB communications system disclosed, is that thetransmitted waveform x(t) can be made to have a nearly continuous powerflow, for example, by using a high chipping rate, where the waveletsg(t) are placed nearly back-to-back. This configuration allows thesystem to operate at low peak voltages, yet produce ample averagetransmit power to operate effectively. As a result, sub-micron geometryCMOS switches, for example, running at one-volt levels, can be used todirectly drive antenna 1, 15, such that the amplifier 25 is notrequired. In this way, the entire radio can be integrated on a singlemonolithic integrated circuit.

[0093] Under certain operating conditions, the system can be operatedwithout the filters 23. If, however, the system is to be operated, forexample, with another radio system, the filters 23 can be used toprovide a notch function to limit interference with other radio systems.In this way, the system can operate simultaneously with other radiosystems, providing advantages over conventional devices that useavalanching type devices connected straight to an antenna, such that itis difficult to include filters therein.

[0094] The UWB transceiver of FIG. 1a or 2 may be used to perform aradio transport function for interfacing with different applications aspart of a stacked protocol architecture. In such a configuration, theUWB transceiver performs signal creation, transmission and receptionfunctions as a communications service to applications that send data tothe transceiver and receive data from the transceiver much like a wiredI/O port. Moreover, the UWB transceiver may be used to provide awireless communications function to any one of a variety of devices thatmay include interconnection to other devices either by way of wiredtechnology or wireless technology. Thus, the UWB transceiver of FIG. 1aor 2 may be used as part of a local area network (LAN) connecting fixedstructures or as part of a wireless personal area network (WPAN)connecting mobile devices, for example. In any such implementation, allor a portion of the present invention may be conveniently implemented ina microprocessor system using conventional general purposemicroprocessors programmed according to the teachings of the presentinvention, as will be apparent to those skilled in the microprocessorsystems art. Appropriate software can be readily prepared by programmersof ordinary skill based on the teachings of the present disclosure, aswill be apparent to those skilled in the software art.

[0095]FIG. 3 illustrates a processor system 301 upon which an embodimentaccording to the present invention may be implemented. The system 301includes a bus 303 or other communication mechanism for communicatinginformation, and a processor 305 coupled with the bus 303 for processingthe information. The processor system 301 also includes a main memory307, such as a random access memory (RAM) or other dynamic storagedevice (e.g., dynamic RAM (DRAM), static RAM (SRAM), synchronous DRAM(SDRAM), flash RAM), coupled to the bus 303 for storing information andinstructions to be executed by the processor 305. In addition, a mainmemory 307 may be used for storing temporary variables or otherintermediate information during execution of instructions to be executedby the processor 305. The system 301 further includes a read only memory(ROM) 309 or other static storage device (e.g., programmable ROM (PROM),erasable PROM (EPROM), and electrically erasable PROM (EEPROM)) coupledto the bus 303 for storing static information and instructions for theprocessor 305. A storage device 311, such as a magnetic disk or opticaldisc, is provided and coupled to the bus 303 for storing information andinstructions.

[0096] The processor system 301 may also include special purpose logicdevices (e.g., application specific integrated circuits (ASICs)) orconfigurable logic devices (e.g, simple programmable logic devices(SPLDs), complex programmable logic devices (CPLDs), or re-programmablefield programmable gate arrays (FPGAs)). Other removable media devices(e.g., a compact disc, a tape, and a removable magneto-optical media) orfixed, high density media drives, may be added to the system 301 usingan appropriate device bus (e.g., a small system interface (SCSI) bus, anenhanced integrated device electronics (IDE) bus, or an ultra-directmemory access (DMA) bus). The system 301 may additionally include acompact disc reader, a compact disc reader-writer unit, or a compactdisc juke box, each of which may be connected to the same device bus oranother device bus.

[0097] The processor system 301 may be coupled via the bus 303 to adisplay 313, such as a cathode ray tube (CRT) or liquid crystal display(LCD) or the like, for displaying information to a system user. Thedisplay 313 may be controlled by a display or graphics card. Theprocessor system 301 includes input devices, such as a keyboard orkeypad 315 and a cursor control 317, for communicating information andcommand selections to the processor 305. The cursor control 317, forexample, is a mouse, a trackball, or cursor direction keys forcommunicating direction information and command selections to theprocessor 305 and for controlling cursor movement on the display 313. Inaddition, a printer may provide printed listings of the data structuresor any other data stored and/or generated by the processor system 301.

[0098] The processor system 301 performs a portion or all of theprocessing steps of the invention in response to the processor 305executing one or more sequences of one or more instructions contained ina memory, such as the main memory 307. Such instructions may be readinto the main memory 307 from another computer-readable medium, such asa storage device 311. One or more processors in a multi-processingarrangement may also be employed to execute the sequences ofinstructions contained in the main memory 307. In alternativeembodiments, hard-wired circuitry may be used in place of or incombination with software instructions. Thus, embodiments are notlimited to any specific combination of hardware circuitry and software.

[0099] As stated above, the processor system 301 includes at least onecomputer readable medium or memory programmed according to the teachingsof the invention and for containing data structures, tables, records, orother data described herein. Stored on any one or on a combination ofcomputer readable media, the present invention includes software forcontrolling the system 301, for driving a device or devices forimplementing the invention, and for enabling the system 301 to interactwith a human user. Such software may include, but is not limited to,device drivers, operating systems, development tools, and applicationssoftware. Such computer readable media further includes the computerprogram product of the present invention for performing all or a portion(if processing is distributed) of the processing performed inimplementing the invention.

[0100] The computer code devices of the present invention may be anyinterpreted or executable code mechanism, including but not limited toscripts, interpretable programs, dynamic link libraries, Java or otherobject oriented classes, and complete executable programs. Moreover,parts of the processing of the present invention may be distributed forbetter performance, reliability, and/or cost.

[0101] The term “computer readable medium” as used herein refers to anymedium that participates in providing instructions to the processor 305for execution. A computer readable medium may take many forms, includingbut not limited to, non-volatile media, volatile media, and transmissionmedia. Non-volatile media includes, for example, optical; magneticdisks, and magneto-optical disks, such as the storage device 311.Volatile media includes dynamic memory, such as the main memory 307.Transmission media includes coaxial cables, copper wire and fiberoptics, including the wires that comprise the bus 303. Transmissionmedia may also take the form of acoustic or light waves, such as thosegenerated during radio wave and infrared data communications.

[0102] Common forms of computer readable media include, for example,hard disks, floppy disks, tape, magneto-optical disks, PROMs (EPROM,EEPROM, Flash EPROM), DRAM, SRAM, SDRAM, or any other magnetic medium,compact disks (e.g., CD-ROM), or any other optical medium, punch cards,paper tape, or other physical medium with patterns of holes, a carrierwave, carrierless transmissions, or any other medium from which a systemcan read.

[0103] Various forms of computer readable media may be involved inproviding one or more sequences of one or more instructions to theprocessor 305 for execution. For example, the instructions may initiallybe carried on a magnetic disk of a remote computer. The remote computercan load the instructions for implementing all or a portion of thepresent invention remotely into a dynamic memory and send theinstructions over a telephone line using a modem. A modem local tosystem 301 may receive the data on the telephone line and use aninfrared transmitter to convert the data to an infrared signal. Aninfrared detector coupled to the bus 303 can receive the data carried inthe infrared signal and place the data on the bus 303. The bus 303carries the data to the main memory 307, from which the processor 305retrieves and executes the instructions. The instructions received bythe main memory 307 may optionally be stored on a storage device 311either before or after execution by the processor 305.

[0104] The processor system 301 also includes a communication interface319 coupled to the bus 303. The communications interface 319 provides atwo-way UWB data communication coupling to a network link 321 that isconnected to a communications network 323 such as a local network (LAN)or personal area network (PAN) 323. For example, the communicationinterface 319 may be a network interface card to attach to any packetswitched UWB-enabled personal area network (PAN) 323. As anotherexample, the communication interface 319 may be a UWB accessibleasymmetrical digital subscriber line (ADSL) card, an integrated servicesdigital network (ISDN) card, or a modem to provide a data communicationconnection to a corresponding type of communications line. Thecommunications interface 319 may also include the hardware to provide atwo-way wireless communications coupling other than a UWB coupling, or ahardwired coupling to the network link 321. Thus, the communicationsinterface 319 may incorporate the UWB transceiver of FIG. 2 as part of auniversal interface that includes hardwired and non-UWB wirelesscommunications coupling to the network link 321.

[0105] The network link 321 typically provides data communicationthrough one or more networks to other data devices. For example, thenetwork link 321 may provide a connection through a LAN to a hostcomputer 325 or to data equipment operated by a service provider, whichprovides data communication services through an IP (Internet Protocol)network 327. Moreover, the network link 321 may provide a connectionthrough a PAN 323 to a mobile device 329 such as a personal digitalassistant (PDA) laptop computer, or cellular telephone. The LAN/PANcommunications network 323 and IP network 327 both use electrical,electromagnetic or optical signals that carry digital data streams. Thesignals through the various networks and the signals on the network link321 and through the communication interface 319, which carry the digitaldata to and from the system 301, are exemplary forms of carrier wavestransporting the information. The processor system 301 can transmitnotifications and receive data, including program code, through thenetwork(s), the network link 321 and the communication interface 319.

[0106] The encoder 21 and waveform generator 17 of the transceiver ofthe present invention function together to create a UWB waveform from adigital data stream by first, multiplying each bit of data in the datastream by an identifying code (e.g., an n-bit user code), therebyexpanding each bit of data into a codeword of data bits equal in lengthto the length of the identifying code. In one embodiment, the codewordis then further processed to create two derivative codewords that arethat are sent to the UWB waveform generator 17 where they are mixed witha pulse generator and recombined through a two-stage mixing processprior to being transmitted via the antenna 15.

[0107] As stated above, the encoder 21 receives a digital data streamfrom an external source via the radio and controller interface 9. Theencoder 21 multiplies each bit of the digital data stream by a usercode, which in one embodiment is a unique sequence of bits correspondingto a particular user. For example, multiplying a user code of ‘11010110’ by a data bit of ‘1’ results in an 8-bit representation of the ‘1’that is identical to the user code, or ‘1101 0110.’ On the other hand,multiplying that same user code by a data bit of ‘0’ results in an 8-bitrepresentation of the ‘0’ that is the 8 bits of the user code inverted,or ‘0010 1001.’

[0108] Continuing with the above example, the encoder 21 multiplies theuser code by each bit of the digital data stream to create a sequence ofn-bit codewords, where n is the length of the user code. Once thedigital data stream has been encoded, the UWB waveform generator 17further processes the sequence of codewords in creating an UWB waveformthat can be transmitted.

[0109]FIG. 4 is a flow chart illustrating a process processing asequence of n-bit codewords to create two derivative codewords that arelater recombined and transmitted via the antenna 15, according to oneembodiment of the present invention. In describing the process set forthin FIG. 4, an example will be used, an illustration of which ispresented along with the flow chart of FIG. 4. In this example, an 8-bitcodeword C 413 will be processed. In the example, C 413 is ‘1101 0110.’

[0110] The process begins at step S401 where k is set to the length ofthe codeword C 413. Accordingly, for the example, k is set to 8 (414).The process then proceeds to step S402 where an internal codeword C_(d)415 is created. The length of C_(d) is equal to two times k in thepresent example. In the example, k was set to 8 at step S401, so thelength of C_(d) 415 is 16. The process then proceeds to step S403 wherethe first half of the internal codeword C_(d) 415 is set to the originalcodeword C 413. Accordingly, following the example, bits 0-7 of internalcodeword C_(d) 415 are set to the values of bits 0-7 of originalcodeword C 413. The process then proceeds to step S404 where the upperhalf of the internal codeword C_(d) 415 is also set to the values of thedata bits in the original codeword C 413. Accordingly, at the completionof step S404, the internal codeword C_(d) 415 includes the originalcodeword C 413 in both the lower and upper halfs.

[0111] Once the internal codeword C_(d) 415 has been created, theprocess proceeds to step S405 where two derivative codewords C₁ 416 andC₂ 417 are created. Both C₁ 416 and C₂ 417 have a length equal to k,which is the length of the original codeword C 413. In the example, thelength of C₁ 416 and C₂ 417 are both equal to 8 bits. In order toinitialize the process, the initial values of C₁ [0] and C₂ [0] are set.Accordingly, at step S406, the 0^(th) bit of C₁ 416 is set to a value of‘1.’ The process then proceeds to step S407 where the 0^(th) bit of C₂417 is set to the 0^(th) bit of the internal codeword C_(d) 415.Following the example, the 0^(th) bit of C₂ 417 is set to ‘1.’ Thealgorithm now initializes a loop, and then enters a loop for populatingall of the subsequent bits of derivative codewords C₁ 416 and C₂ 417. Atstep S408, the loop is initialized by setting an index n=1. The processthen proceeds to step S409 where the n^(th) bit of derivative codewordC₂ 417 is set equal to the value of C₁ [n−1] XNOR C_(d) [2n−1]. As wouldbe understood by one of ordinary skill in the digital logic art, an XNORfunction results in a ‘1’ when the two inputs have the same value. Asshown in the example, applying step S409 for n=1, the 1^(st) bit ofderivative codeword C2 417 is set to a value of 1, which is equal to C₁[0] XNOR C_(d) [1]. The process then proceeds to step S410 where then^(th) bit of C₁ 416 is set to C₂ [n] XNOR C_(d) [2n]. In the example,for n=1, the 1^(st) bit of C₁ 416 is set to ‘0.’

[0112] The process then proceeds to step S411 where it is determined ifthe end of the sequence of codewords has been reached. If the end of thesequence of codewords has been reached (i.e., ‘Yes’ at step S411), theprocess ends. If however, the end of the sequence of codewords has notbeen reached (i.e., ‘No’ at step S411), the process proceeds to stepS412 where the index of the loop is incremented. After the index of theloop has been incremented, at step S412, the process returns to the topof the loop, step S409, so that subsequent bits of the derived codewordsC₁ 416 and C₂ 417 may be calculated.

[0113] As would be understood by one of ordinary skill in the encodingart or digital design art, steps S401-S408 are used to initialize theprocess. Accordingly, it can be seen that for a stream of codewords C413, once step S409 has been reached, the process will continue in itsloop until all bits of the stream of codewords have been processed. Itwould not be necessary to execute steps S401-S408 again unless therewere a break in the data stream, thereby creating a need to reinitializethe algorithm.

[0114]FIGS. 5, 6, 8, and 8A illustrate the circuit components used inimplementing one embodiment of the present invention. In thisembodiment, two derived codewords, such as C₁ 416 and C₂ 417 describedby the algorithm in FIG. 4, are used in a two-stage mixer waveformgenerator. In this embodiment, the use of two derivative codewordsallows for decreased power consumption within the circuitry, and thetwo-stage mixer waveform generator creates UWB waveforms that do notcontain unwanted spectral spikes.

[0115]FIG. 5 is a process flow diagram showing an original codeword C413 being split by a splitter 501 into two codewords, C_(even) 502containing the even bits of the original codeword C 413, and C_(odd)503, containing the odd bits of the original codeword C 413. As shown inFIG. 5, the original codeword C 413 enters the splitter 501 at 100megabits per second (Mb/s). The splitter 501 samples C 413 at 100 Mb/sto create two codewords, C_(even) 502 and C_(odd) 503, each at 50 Mb/s.The clock CLK 504 samples the incoming codeword C 413 at 100 Mb/splacing the first sample into position 0 of C_(even) 502, and the secondsample into position 0 of C_(odd) 503, and so on. Accordingly, sinceeach of the two resultant code words, C_(even) 502 and C_(odd) 503receive a new data bit on every other clock pulse, the resultantcodewords contain every other bit of the original codeword C 413 atone-half the clock rate of the original codeword C 413, or 50 Mb/s inthis example. Also, it should be noted that since C_(odd) 503 receivesits first bit on the second clock pulse, the resultant codewords,C_(even) 502 and C_(odd) 503 are 90° out of phase with one another. Theresults of the splitter 501 (i.e., C_(even) 502 and C_(odd) 503) arethen provided to a logic circuit to create the two derivate codewords C₁416 and C₂ 417 that were created by the process described in FIG. 4.

[0116]FIG. 6 shows a logic circuit for creating the two derivedcodewords C₁ 416 and C₂ 417 from the C_(even) 502 and C_(odd) 503codewords created by the splitter 501 in FIG. 5. As shown in FIG. 6, thelogic circuit includes two exclusive NOR (XNOR) gates 603 and 604, twolatches 605 and 606, and two clocks CLK₁ 601 and CLK₂ 602. CLK₁ 601 andCLK₂ 602 are 90° out of phase with one another. By processing twohalf-speed data streams, C_(even) 502 and C_(odd) 503, the powerconsumption of this circuit is lower than that required to process adata stream running at twice the rate. Low power consumption isfavorable when configuring a transceiver for mobile devices such as PDAsand mobile telephones since maximizing battery life is a design goal.The logic circuit of FIG. 6 generates the two derived code words C₁ 416and C₂ 417 as described in the context of the process flow in FIG. 4.Both C₁ 416 and C₂ 417 are the same length as the original codeword C413, are at half the data rate of the original codeword C 413, and are90° out of phase with one another. Once the derived codewords have beencreated, they are sent to a two-stage mixer by which a UWB waveform isgenerated.

[0117]FIG. 7 is a schematic diagram of a two-stage mixer for generatinga UWB waveform in one embodiment of the present invention. As shown inFIG. 7, derived codeword C₁ 416 is mixed at a first mixer 701 with theoutput of an early/late pulse generator 702. The early/late pulse streamruns at twice the chipping rate of derived codeword C₁ 416. In thisexample, C₁ 416 is a data stream at 50 Mb/s, and the early/late pulsestream 702 is at 100 Mb/s. The output of the simple wavelet generator707 is a pulse stream of single-cycle bi-phase wavelets.

[0118] In other embodiments, the simple wavelet generator 707 may bereplaced by more circuits to implement more complex modulation schemessuch as those described in co-pending application incorporated byreference above Ser. No. ______, entitled SYSTEM AND METHOD FORGENERATING ULTRA WIDEBAND PULSES (Attorney docket number 197023US). Forexample, the output of the wavelet generator may be a pulse stream ofpulses having a variety of shapes and/or amplitudes. By controlling theshapes of the wavelets generated, multiple bits of data may be encodedtherein.

[0119]FIG. 8 is a schematic diagram of a circuit for generating a UWBwaveform in one embodiment of the present invention. As shown in FIG. 8,data 416 is mixed at a first mixer 701 with the outputs of an early/latepulse generator 200. The early/late pulse streams run at the chippingrate. The chipping rate can be the same as the data rate of derivedinput data 416, in which case a single wavelet, or chip, is transmittedfor each bit. The chipping rate may also be an integer multiple of thedata rate of the derived input data 416. In such a case, each bit ismade up of a predetermined number of bits. For example, if the datastream 416 is at 50 Mb/s and there are 16 chips per bit, then theearly/late pulse streams 286, 288 are at 800 MHz.

[0120] As shown in FIG. 8, the pulse generator 200 receives its inputfrom a differential clock 210 which generates a pulse 203, which isdifferentially transmitted on lines 202 and 204. Input lines 202, 204feed into the first of a set of seven buffers 212, 214, 216, 218, 220,222, and 224 connected in series. While seven buffers are shown in thisfirst series-connected set of buffers, it would be understood by one ofordinary skill in the art that other numbers of buffers could be used toprovide a different time delay through the set. Buffers 214 and 216 areconnected in series via lines 224, 226. In the preferred embodimentdisclosed in FIG. 8, data lines 228 and 230 branch off from lines 224and 226 respectively and serve as inputs to buffer 244. The output ofbuffers 242 and 244 serve as inputs via lines 246, 248 to an exclusiveOR gate 250, which generates a pulse 205. In another embodiment, an ANDgate could be used in place of the exclusive OR gate 250, where theinverting output of one of either buffer 242 or buffer 244 is used tofeed the AND gate 600 instead of the non-inverting output, as shown inFIG. 8A. An AND gate 600 provides some advantages since the AND gate 600generates a pulse only on the rise of the pulse, whereas an exclusive ORgate 250 gives a pulse both on the rise and the fall of the pulse.Therefore, timing of the circuit is less difficult to implement with anAND gate. The output of the exclusive OR gate 250 is a differentialpulse 205 which feeds into another series-connected set of buffers, inthis example, seven buffers 260, 262, 264, 266, 268, 270, and 282 vialines 252, 254. Buffers 262 and 264 are connected in series via lines253 and 255. In the preferred embodiment disclosed in FIG. 8, data lines276 and 278 branch off from lines 253 and 255 respectively and serve asinputs to buffer 280. The output from buffers 280 and 282 feed intodifferential mixer 701 via lines 286 and 288. The differential mixer 701receives the data stream from encoder 21 over lines 292, 294.

[0121] The function of the pulse generator 200 shown in FIG. 8 will nowbe described. The clock 210 generates a differential semi-square waveclock signal 203, which are transmitted over lines 202, 204 to buffer212. Buffer 212 serves to amplify, saturate, and generally square up theincoming signal, and then buffer 214 squares it up some more. Thetransmission of the clock signal 203 through two paths, one throughbuffers 216, 218, 220, 222, and 242, and the other through buffer 244,causes the clock signal to reach the output of buffer 244 before itreaches the output of buffer 242. In other words, the output of buffer244 leads the output of buffer 242 by the delay accumulated in buffers216, 218, 220, and 222. Since the inputs to the exclusive OR gate 250are matched except at the clock transitions, pulse 205 is generated atthe output of exclusive OR gate 250 at each transition of the clock. Thepulse stream, therefore, is at twice the clock frequency because anexclusive OR gate 250 generates a pulse on both leading and trailingclock transitions.

[0122] In another embodiment, an AND gate 600 could be used in place ofthe exclusive OR gate 250, where the inverting output of either buffer242 or buffer 244 is used to feed the AND gate 600 instead of thenon-inverting output, as shown in FIG. 8A. Since the inputs to the ANDgate 600 are mismatched except at the leading clock edge transition (ifthe inverting output of buffer 242 is used), or the trailing clock edgetransition (if the inverting output of buffer 244 is used) the output ofthe AND gate 600 is a pulse stream that equals the clock frequency. AnAND gate 600 provides some advantages since the AND gate 600 generates apulse only on the rise or fall of the pulse, whereas an exclusive ORgate 250 gives a pulse both on the rise and the fall of the pulse.Therefore, the duty-cycle of the clock does not have to be exactly 50%in order to have an equal time period between all pulses. Instead, theduty cycle can be anything, making the circuit is less difficult toimplement.

[0123] The pulse 205 is transmitted over differential lines 252 and 254to buffer 260. Buffer 260 serves to amplify, saturate, and generallysquare up the pulse and then buffer 262 squares it up some more. Thetransmission of the pulse 205 through two paths, one path viadifferential lines 253 and 255 through buffers 264, 266, 268, 270, and282, and the other path via differential lines 246 and 248 throughbuffer 280 causes the pulse 205 to reach the output of buffer 280 beforeit reaches the output of buffer 282. In other words, output 286 ofbuffer 280 leads output 288 of buffer 282 by the delay accumulated inbuffers 264, 266, 268, and 270. Accordingly, line 286 has an early pulseand line 288 has a late pulse, making pulse streams 203 a and 203 brespectively.

[0124] The early pulse on line 286 feeds the non-inverting differentialLO input of multiplier 701. The late pulse on line 288 feeds theinverting differential LO input of multiplier 701. The differentialdata-source 416 generates data, which is differentially transmitted onlines 292 and 294. Input lines 292 and 294 feed into the first of a setof two series-connected buffers 296 and 298. The differential outputdata from buffer 298 drives the differential RF-input port of multiplier701. Given the data on the RF-port of multiplier 701, and the early andlate pulse on the non-inverting and inverting input lines of thedifferential LO-port of multiplier 701, the output of the multiplier isthe desired wavelet shape. When the data is a ‘1,’ the output wavelethas a ground-positive-negative-ground shape, and when the data is a ‘0,’the output wavelet has a ground-negative-positive-ground shape.

[0125]FIG. 9A is a schematic diagram of a transistor-based Gilbert celldifferential mixer used in one embodiment of the present invention. Inthis embodiment, it is shown that mixing the resultant early/late pulsestreams 286, 288 generated by the pulse generator 200 shown in FIG. 8,the result is a sequence of bi-phase wavelets corresponding to the inputdata 416. In other embodiments of the present invention, the waveletsgenerated may have different shapes, such as, but not limited tomultilevel and/or quad-phase wavelets. Accordingly, if differentencoding schemes are used, different amounts of information may beencoded in any single wavelet, thereby affecting the data ratesachievable at a given chip rate.

[0126] As would be understood by one of ordinary skill in the art, FIG.9A is a schematic diagram of a bipolar transistor-based Gilbert celldifferential multiplier. It is capable of multiplying the differentialsignal across 330 and 332, by the differential signal across 286 and288, the product appearing across the differential output 340 and 342.It includes a current mirror 704, which provides a current that will besteered between the differential output nodes 340 and 342. Differentialpair 706 steers the current between two paths, the first path todifferential pair 710, and the second path to differential pair 708.Differential pair 710 and differential pair 708 are connected todifferential input lines 330 and 332, and to the differential outputnodes 340 and 342 so as to oppose one another, (i.e., if thedifferential input 330 is high, then differential pair 710 steers itscurrent to pull 342 low but differential pair 708 steers its current topull 342 high). The pair that dominates is determined by which has themost current available to it, which is determined by differential pair706. Differential pair 706 accepts differential inputs 286 and 288. When286 is higher than 288, the current is steered to differential pair 710and the output 340 is inverted from input 330 (i.e., multiplying by −1).When 288 is higher than 286, the current is steered to differential pair708 and the output 340 is not inverted from input 330 (i.e., multiplyingby +1). When 286 is equal to 288, the current is steered identically tothe output nodes 340 and 342 so that the output is independent of theinput 330 and 332 (i.e., multiplying by zero). Accordingly, by mixingthe early/late pulses shown in FIG. 9B with a high input to A 330, theoutput waveform will be of the form shown in FIG. 9C. On the other hand,by mixing the early/late pulses shown in FIG. 9B with a low input to A330, the output waveform will be of the form shown in FIG. 9D.

[0127] In other embodiments, the wavelet generating function of thedifferential mixer 701 is accomplished using, for example, bridgecircuits using switches. The can be electronically controlled switchessuch as an FET-bridge mixer 702 of FIG. 9E or a diode-bridge mixer 703of FIG. 9F. In other embodiments, the switches are mechanical, using,for example, MEM (micro electromechanical machine) technology, oroptically driven switches such as a bulk semiconductor material. Invarious embodiments of the present invention, all of the ports of themixer are differential or all of the ports of the mixer accept digitalinputs, or both.

[0128] Using a differential mixer to generate the UWB wavelets accordingto the present invention provides advantages over conventional methods.For example, using a conventional method of passing a pulse through oneor more transmission line stubs to create a waveform includes usingcomponents (i.e., the stubs) that are not integratable. Accordingly, theconventional approach uses up more space, which is of a premium whendesigning UWB wireless devices. Accordingly, by using highlyintegratable components, such as transistor-based differentialcomponents in combination with the pulse generator 200 described above,the present invention provides a highly integratable solution forcreating UWB wavelets, even into the microwave regime.

[0129] Returning to FIG. 7, the output of the simple wavelet generator707 in this embodiment is a series of wavelets at twice the rate of theinput derivative codeword C₁ 416. Accordingly, for each bit of data inthe codeword C₁ 416, there are two wavelets output from the firstdifferential mixer 701. For example, if the first bit of the inputderivative codeword C₁ 416 is a ‘1,’ the output of the firstdifferential mixer 701 will be two wavelets, each looking similar to thewaveform shown in FIG. 9c. On the other hand, if the first bit inputfrom the derivative codeword C₁ 416 is a ‘0,’ the output of the firstdifferential mixer 701 will be two wavelets, each looking similar to thewaveform shown in FIG. 9D.

[0130]FIG. 10 shows a timing chart of the simple wavelet generator 707using the same example as was used in the description of the algorithmin FIG. 4. As shown in FIG. 10, the input derivative codeword C₁ 416 isan 8-bit codeword (i.e., ‘1011 0100’), at 50 Mbit/s. The simple waveletgenerator 707 provides a series of early and late pulses that are mixedwith the derivative codeword C₁ 416 at the first differential mixer 701.The output of the first differential mixer 706 is a series of twoindividual wavelets per bit of data from the derivative codeword C₁ 416.The wavelets are positive then negative as shown in FIG. 9Ccorresponding to each data bit that is a ‘1.’ On the other hand, fordata bits that are ‘0,’ the wavelets are inverted, thereby similar tothe waveform shown in FIG. 9D. Accordingly, the output of the simplewavelet generator 707 is a series of data-encoded wavelets that areprovided as an input into the second differential mixer 703, shown inFIG. 7.

[0131]FIGS. 11A and 11B illustrate the spectral spikes that are createdby non-ideal analog devices such as the first differential mixer 701. Asshown in FIG. 11A, the output of the first differential mixer includesnot only the desired signal 1101, shown in the frequency domain, butalso unwanted spectral spikes at the fundamental frequency f₁ 1102, andits harmonics (e.g., f₂ 1103, f₃ 1104, and f₄ 1105), as well as othernoise generated by the first differential mixer 701. By creating twoderivative codewords C₁ 416 and C₂ 417, the inventors have developed anapproach for using a two-stage mixing technique that will sufficientlyspread the spectrum of the unwanted spikes generated at the firstdifferential mixer 701. By mixing the output of the first differentialmixer 701 with the sufficiently-white second derivative codeword C₂ 417at a second differential mixer 703, the energy contained in the unwantedspikes is whitened (i.e., spread over a large band). As illustrated inFIG. 11B, the spectral spikes 1106 have been spread, or “whitened,” sothat they are below the signal level of the desired signal 1101. Thebenefits of the two-stage mixing technique may be gained through variousembodiments of the present invention, as would be well understood by oneof ordinary skill in the digital signal processing art based on thepresent discussion. The embodiment shown in FIG. 7 using two derivativecodewords C₁ 416 and C₂ 417 is only one exemplary one technique forusing a two-stage mixing approach to eliminate spurious spectral spikescaused by non-ideal analog devices such as the differential mixers 701and 703 used to generate a UWB waveform.

[0132] Returning to FIG. 7, the output of the first differential mixer706 is mixed with the second derivative codeword C₂ 417 at the seconddifferential mixer 703. As described above, the second derivativecodeword C₂ 417 is at half the data rate of the original codeword C 413,is 90° out of phase with the first derivative codeword C₁, andaccordingly, at half the data rate of the output of the firstdifferential mixer 706. The second differential mixer 703 is the sametype of device as the first differential mixer 701.

[0133]FIG. 12 is a timing chart of the second differential mixer 703. Asshown in FIG. 12, the output of the first differential mixer 706 is aseries of wavelets at twice the clock speed of the second derivativecodeword C₂ 417. Furthermore, the output of the first mixer 706 is 90°out of phase with the second derivative codeword C₂ 417, as discussedabove. The second differential mixer 703 will invert the waveform outputfrom the first differential mixer 701 when the bit of the secondderivative codeword C₂ 417 is a ‘0.’ When the data bit of the secondderivative codeword C₂ 417 is a ‘1,’ the output of the firstdifferential mixer 706 will not be inverted at the second differentialmixer 703. The output of the second differential mixer 707 will be aseries of wavelets, each wavelet corresponding to a ‘1’ if the wavelethas a shape similar to that shown in FIG. 9C, or corresponding to a ‘0’if the wavelet has a form similar to that shown in FIG. 9D. The datarate of the output of the second differential mixer 707 will be equal tothat of the original codeword C 413.

[0134] To complete the example, the resultant waveform output from thesecond differential mixer 707 can be decoded into ones and zeros 1001 asshown in FIG. 12. When comparing the decoded data 1001 with the originalcodeword C 413, it can be seen that an inverted representation of theoriginal codeword C 413 is contained in the decoded data 1001. It shouldbe noted that a continuous stream of data were used in the example,after an initialization of the algorithm had taken place, a continuousstream of inverted input data would be contained in the output of thesecond differential mixer 707.

[0135] Returning to FIG. 7, the output of the second differential mixer707 is passed through an inverting amplifier 704 and then coupled to anantenna 705 so that the data may be propagated through space.

[0136]FIG. 13 shows another embodiment of the present invention, whereit is not necessary to generate derivative codewords such as C₁ 416 andC₂ 417 in order to gain the advantages of the two-stage mixing approach.As shown in FIG. 13, a sufficiently-white random sequence 1301 iscombined with the original data stream 1302 at an exclusive OR (XOR)gate 1303. The output of the XOR gate 1303 is mixed with the output ofthe early/late pulse generator 702, as shown in FIG. 7, at a firstdifferential mixer 701. The output of the first differential mixer 706is mixed with the random pulse sequence 1301, which has been delayed bythe delay 1304 to account for the XOR gate 1303 and the firstdifferential mixer 701, at the second differential mixer 703 to createan output waveform 707 that can be passed through an inverting amplifier704 and then coupled to an antenna 705. By mixing the noisy pulse stream1301 with the data 1302 and mixing the output of the first differentialmixer 701 with the same noisy pulse stream 1301, the spectral spikesproduced by the first differential mixer 701 will be whitened at thesecond differential mixer 703. As would be understood by one of ordinaryskill in the digital signal processing art in light of the presentdescription, various other embodiments of the two-stage mixing approachmay be used to achieve similar advantageous results.

[0137]FIG. 14 is a schematic diagram of a generalized two-stage mixingcircuit for achieving noise cancellation in an ultra widebandtransmitter according to the present invention. As shown in FIG. 14, thetransmitter includes a NRZ data source 1400, a de-spur code generator1401, a first mixer 1402, a pulse generator 1403, a second mixer 1404,an amplifier 1405, and an antenna 1406. As discussed above, the presentinvention uses a two-stage mixing to cancel self-noise caused by thenon-ideal analog mixers. The concepts taught herein provide advantagesto UWB systems regardless of the encoding or modulation scheme beingused.

[0138] By changing the circuitry of the de-spur code generator 1401 andthe pulse generator 1403 many different encoding and modulation schemesmay be used, such as those described in relation to FIGS. 7 and 13, aswell as the various modulation techniques described in co-pendingapplication Ser. No. ______, entitled SYSTEM AND METHOD FOR GENERATINGULTRA WIDEBAND PULSES (Attorney docket number 197023US8). For example,the transmitted UWB wavelets coupled to the antenna 1406 may, forexample, be bi-phase wavelets, multi-level bi-phase wavelets, quad-phasewavelets, multi-level quad-phase wavelets, or other shapes used toencode the NRZ data source 1400. As is taught in the above-referencedco-pending application Ser. No. ______, entitled SYSTEM AND METHOD FORGENERATING ULTRA WIDEBAND PULSES (Attorney docket number 197023US8),amplitude and phase information may be applied by the de-spur codegenerator 1401, the pulse generator 1403, or a combination of both.

[0139] The de-spur code generator 1401 is configured such that when thetwo outputs are mixed together, the resultant waveform is an encodedrepresentation of the NRZ data source 1400. An example of this wasillustrated in the embodiment presented in FIG. 7 wherein two derivedcodewords were produced that when recombined at the second mixer 703results in a sequence of shaped UWB wavelets having the data streamencoded therein. As would be understood by one of ordinary skill in theart in light of the present discussion and the teachings of theabove-referenced co-pending application Ser. No. ______, entitled SYSTEMAND METHOD FOR GENERATING ULTRA WIDEBAND PULSES (Attorney docket number197023US8), the de-spur code generator 1401 in combination with thepulse generator 1403 could implement a variety of schemes for achievingthe advantageous results described herein.

[0140] Obviously, numerous modifications and variations of the presentinvention are possible in light of the above teachings. It is thereforeto be understood that within the scope of the appended claims, theinvention may be practiced otherwise than as specifically describedherein.

1. A system for suppressing self-noise in an ultra wideband wavelettransmitter, comprising: a first differential mixer having a firstinput, a second input and an output, said second input being adifferential input having a first differential input and a seconddifferential input, said first input being configured to receivenon-return-to-zero data from a source; a second differential mixerhaving a first input, a second input and an output, said second inputbeing a differential input having a first differential input and asecond differential input; an exclusive OR circuit having a first inputconfigured to receive said data, a second input configured to receive awhitening sequence from a noise source, and an output; and a pulsegenerator configured to generate a pulse sequence having at least twopulses in a predetermined pattern; wherein said non-return-to-zero datasource and said white pseudo-random non-return-to-zero noise sourcebeing input to said exclusive OR circuit, said output of said exclusiveOR circuit being input to the first input of said first differentialmixer, at least one of said at least two pulses generated by said pulsegenerator being input to the first differential input of said secondinput of said first differential mixer, and a different at least one ofsaid at least two pulses being input to the second differential input ofsaid second input of said first differential mixer, said output of saidfirst differential mixer being input to the first input of said seconddifferential mixer, said whitening sequence being input to the firstdifferential input of said second input of said second differentialmixer, and said output of said second differential mixer providing saidultra wideband wavelets.
 2. A system for suppressing self-noise in anultra wideband wavelet transmitter, comprising: a first differentialmixer having a first input, a second input and an output, said secondinput being a differential input having a first differential input and asecond differential input, said first input being configured to receivenon-return-to-zero data from a source at a predetermined chipping rate;a second differential mixer having a first input, a second input and anoutput, said second input being a differential input having a firstdifferential input and a second differential input; an encoder; and apulse generator configured to generate a pulse sequence having at leasttwo pulses in a predetermined pattern; wherein said encoder beingconfigured to encode the non-return-to-zero data source into a firstderivative codeword at one half of said predetermined chipping rate anda second derivative codeword at one half of said predetermined chippingrate and 90° out of phase with said first derivative codeword, saidfirst derivative codeword being input to the first input of said firstdifferential mixer, at least one of said at least two pulses generatedby said pulse generator being input to the first differential input ofsaid second input of said first differential mixer, and another of saidat least two pulses being input to the second differential input of saidsecond input of said first differential mixer, said output of said firstdifferential mixer being input to the first input of said seconddifferential mixer, said second derivative codeword being input to thefirst differential input of said second input of said seconddifferential mixer, and said output of said second differential mixerbeing configured to provide ultra wideband wavelets having encodedtherein the non-return-to-zero data at the predetermined chipping rate.3. A system for suppressing self-noise in an ultra wideband wavelettransmitter, comprising: a de-spur code generator having an inputconfigured to receive a non-return-to-zero data stream, and configuredto encode the non-return-to-zero data stream and to generate a firstoutput and a second output such that mixing the first output with thesecond output produces an encoded representation of thenon-return-to-zero data stream; a pulse generator configured to generatea pulse sequence having at least two pulses in a predetermined pattern;a first mixer having a first input, a second input and an output, saidsecond input being a differential input having a first differentialinput and a second differential input, the first input being configuredto receive the first output from the de-spur code generator, the firstdifferential input being configured to receive at least one of the atleast two pulses, and the second differential input being configured toreceive another one of the at least two pulses; and a second mixerhaving a first input, a second input and an output, the first inputbeing connected to the output of the first mixer, the second input beingconfigured to receive the second output from the de-spur code generator,wherein the output of the second mixer is a sequence of shaped ultrawideband wavelets having encoded therein the non-return-to-zero data.